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EXP-6
CHEM 233L
AKAC (Aldehyde, Ketone, Alcohol, Carboxylic Acid) UNKNOWN IDENTIFICATION
Introduction:
The purpose of this experiment was to identify an unknown from a possible list by
performing a series of qualitative tests. The unknown was one of the four functional
groups: aldehyde, ketone, alcohol or carboxylic acid (AKAC). Additional chemical and
physical properties were used to narrow down the possibilities and to determine the
unknown.
Functional Group Classification Tests:
It is recommended to perform the following tests in order to narrow down your
possibilities. A negative result is as important as a positive result. It is also recommended
that you perform your tests with a known compound to learn to interpret a positive or
negative test.
Test Name
1 Solubility of water
1. Test the solubility of your unknown in water using a
small test tube.
2. Dissolve 30 mg of your unknown in 1 ml of water.
3. The solid should dissolve completely.
4. If your unknown is a liquid, weigh 5 drops and based on
the weight, add the required amount to keep the reaction
of 0.030 g/ ml.
5. Do not discard this solution, it is used for the following
test.
Characteristics
 Most compounds are insoluble.
Compounds of 5 carbons or less
are water-soluble.
 For example: both 1-butanol
and 1-pentanol were water
soluble, but 1-hexanol is not.
2 pH
 Most compound were respected
1. Check the pH of the solution prepared above.
to be neutral (pH 6 or above)
2. If the compound was not water soluble, try to still check  Carboxylic acid will have a pH
the pH.
between 3-6.
If an acidic pH was given, save the solution for the next
step.
3 Reactivity towards aq. NaHCO3
Carboxylic acids react with aq.
NaHCO3 , in an acid-base reaction,
producing a water-soluble sodium
RCO2H + NaHCO3
R CO2Na + H2O + CO2 (g)
1. Add small amounts of solid NaHCO3 carefully to the salt, water and liberating CO2 gas.
unknown sample and dissolve in water.
2. Observe the formation of CO2 bubbles or fizzing.
3. If you are not sure, use a larger sample and look more
carefully.
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4 2,4-Dinitrophenyl Hydrazine (2,4-DNP)
1.
2.
3.
4.
5.
6.
7.
Dissolve 2 drops of a liquid or 100 mg of a solid in 2
ml of 95% ethanol.
Add 2,4-Dinitrophenyl Hydrazine to this solution.
Shake the mixture vigorously.
If a precipitate does not form immediately, letthe
mixture stand for 15 minutes.
If a yellow or orange precipitate forms, repeat the
reaction with double the amount of sample used.
Chill the precipitate and isolate by filtration.
Submit your 2,4- Dinitrophenyl Hydrazine derivative
with your report.
Both aldehydes and ketones react
with 2,4- Dinitrophenyl Hydrazine
to form a hydrazone derivative.
When a positive result is observed
a yellow or orange precipitate is
observed in a couple of minutes.
5 Chromic Acid Test ( Jones’ test)
 RCH2—OH + H2CrO4
precipitate or Aldehyde
O
OH
H2CrO4
R
R
RCO2 + Green solution
or
+ Green solution or precipitate
R
 R
1. Dissolve about 3 drops of liquid or 50 mg of solid
alcohol or aldehyde in 2 ml of acetone.
2. Add 3 drops of Jones reagent and shake the tube to mix
the mixture.
3. Observe a color change within one minute. A positive
test is confirmed when the red color of chromium (VI)
changes to green or blue-green emulsion or precipitate.
6 Tollen’s Test ( Silver Mirror Test)
Aldehydes react with Silver ion in
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O
R
+ Ag(NH3)2 +
O
2HO-
H
R
+
Ag(s) + H O+ NH3
2
O-NH4
1. Tollen’s reagent consists of two solutions: solution
A and B. Solution A contains 5% aqueous silver
nitrate, solution B contain 10% aq. KOH.
2. Prepare Tollen’s reagent by mixing solution A (2.5
g of silver nitrate in 43 ml of distilled water) and
solution B (3g of potassium hydroxide in 42 ml of
distilled water)
3. Obtain 3ml of both solution A and B.
4. To 3 ml of solution A, add concentrated ammonium
hydroxide solution drop wise until the initial brown
precipitate (Ag2O) begins to clear.
5. The solution should be grayish and almost clear.
Add 3ml of solution B into solution A and add
concentrated ammonium hydroxide drop wise until
the solution is almost clear.
6. To test your suspected aldehyde, 1ml of Tollen’s
reagent to 5 drops of your known. The formation of
a silver mirror on the walls of the test tube represents
a positive test. If no reaction occurs within 5 minutes
at room temperature, warm the mixture with a
beaker of boiling water.
7 Lucas Test
ClOH
R
+
H+
1.
R
OH2
R+
R
Cl
Add 2 drops of the unknown to 2 ml of the Lucas
reagent. Stir the mixture.
2. The formation of a second (insoluble) top layer was
observed. This test is limited to alcohols that they
are initially soluble in water.
8 Iodoform Test
base (Tollen’s reagent) forming
carboxylic acids. A positive test is
characterized by the formation of
a permanent shiny silver mirror
due to the formation of solid
silver.
The Lucas test is a mixture of HCl
and ZnCl2. The Lucas test is used
for the classification of alcohols
into primary, secondary, and
tertiary.
Iodine in base reacts with methyl
ketones or methyl alcohols
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1. If your unknown is water soluble, dissolve 3 drops
of your liquid unknown, or dissolve 50 mg of your
solid unknown in 2 ml of water.
2. Add 2 ml of 3M NaOH followed by 2 ml of the
iodine solution.
3. If your unknown is insoluble in water, dissolve in 2
ml of dioxane and proceed as above, and then dilute
the mixture with 10 ml of water after the addition of
the iodine solution.
A yellow solid should form within minutes. Isolate the
yellow solid and submit with your report.
producing a carboxylic acid and
iodoform (CHI3
A positive result is obtained with
the formation of a yellow
precipitate due to the formation of
iodoform, CHI3. If you obtain a
positive result, the precipitated
yellow solid was isolated and
submitted it with your report as
evidence of your work.
Compound with following
structure give a positive test.
O
R
9 Ignition Test
1. Place a small amount (10mg) of the solid unknown
or a few drops of the liquid on a spatula.
2. Bring the spatula near a Bunsen burner, whereas
most aromatic compounds burn with a smoky flame.
CH3
R
CH3
The ignition test is used to
distinguish between aromatic
versus no-aromatic compounds.
Many alkanes and their derivatives
burn with a clean yellow or bluish
flame, whereas most aromatic
compounds burn with a smoky
flame.
Safety Notes:
 Avoid contact to eyes, skin and clothing.
 Be careful when using a Bunsen burner and a heating mantle.
Reference:
www.chemfinder.com
Lab #6 handout.
OH